1. Field of the Invention
The systems and methods of this invention relate to electrical tissue stimulation treatments using implantable devices. Specifically, the present invention relates to systems and methods for providing such stimulation without the use of conventional lead/electrode systems for stimulating tissues such as, bone, brain, spine, stomach, nerve, and cochlea for therapeutic purposes.
2. Description of the Background Art
Electrical stimulation of body tissues is used for treatment of both chronic and acute medical conditions. Perhaps the best known medical application of electrical stimulation is that used to initiate a heart beat by stimulating cardiac tissue for the treatment of arrhythmias. Among several other examples, direct muscle stimulation is used to initiate contraction of functional muscles in paraplegics; peripheral muscle stimulation is known to accelerate healing of strains and tears; bone stimulation is likewise indicated to increase the rate of bone regrowth and repair in fractures; and nerve stimulation is used to alleviate chronic pain. Furthermore, there is encouraging research in the use of electrical stimulation to treat a variety of nerve and brain conditions, such as essential tremor, Parkinson's disease, migraine headaches, functional deficits due to stroke, and epileptic seizures. Another area where electrical stimulation is used to treat a medical condition is the electrical stimulation of the cochlea of the ear and to cochlear nerves and to regions proximal to cochlear nerves of the ear as a treatment for hearing loss.
For electrical tissue stimulation, generally, the system comprises a transmitter or a controller and a stimulator. Additionally, there may be a programmer that communicates with the transmitter and exchanges stimulation parameters. The transmitter and the stimulator may be external or implanted. In the embodiment where leads connect the transmitter and the stimulator, electrodes are present on the leads and are in contact with the tissue that is to be stimulated. Understandably, there are variations in the details of the devices, depending on the tissue to be stimulated. Various devices and arrangements that are currently used for stimulating different tissues and their shortcomings are described below.
In current practice, implanted electrical energy sources and electrode/lead wire systems are typically used to directly stimulate tissue at the desired site. Such implanted electrode/lead wires exhibit significant problems, such as infection, lead failure, and electrode/lead dislodgement. If the leads were externalized, then the entry/exit site in the skin must be carefully managed to avoid infection. Various approaches for different tissue stimulations that are prevalent, and their shortcomings, are described below.
Bone Stimulation
Bone stimulation is used to increase the rate of bone regrowth, repair, fusion of bones or bone grafts. Commonly implanted devices utilizing electrical stimulation for treatment in bone fusion are made by such companies as Biomet (Electro-Biology, Inc. (EBI)). Similarly, ultrasound energy has been used as a noninvasive therapeutic healing application in bone treatments, such as in the Exogen Bone Healing System made by Smith&Nephew.
Electrical bone growth stimulation (EBGS) generally refers to the treatment of bone fusion or repair using electrical current (direct current or alternating current). Currently, invasive use of these devices involves surgical implantation of a current generator in an intramuscular or subcutaneous space, while an electrode is implanted within the fragments of bone or bone graft at the bone fusion site. Limited by battery utilization, the implantable device typically remains functional for six to nine months after implantation; alternatively, it can be adapted to be rechargeable. Although the current generator is removed in a second surgical procedure when stimulation is completed, the electrode may or may not be removed. Noninvasive approaches that apply an electrical or electro-magnetic field transcutaneously to the bone area via externally worn devices are also available. Ultrasonic bone growth stimulation (UBGS) generally refers to the treatment of bone fusion and repair using low-intensity ultrasound as an energy source and the ultrasound energy is externally applied. In noninvasive electrical applications, electrical devices require patient interaction to apply and remove electrodes. Compliance with noninvasive EBGS and UBGS is often an issue because it requires the patient to apply the therapy at a prescribed regimen and intensity. Patients may not keep batteries charged, may not comply with instructions, may fail to wear electrodes for required durations, or may adjust intensities inappropriately for the electrical bone stimulation therapy or ultrasound therapy application to be effective.
EBGS is used as an adjunct to spinal fusion surgery, with or without associated devices such as cages or screws to enhance the chances of obtaining a solid spinal fusion. EBGS has also been used as a treatment of failed spinal fusion surgery (i.e., salvage therapy). Pedicle screws and interbone cages are devices used to facilitate fusion. The role of electrical stimulation of the spine for instrumented fusions, and also in patients not considered at high risk for fusion failure, is still emerging. EBGS may be considered medically necessary as an adjunct to spinal fusion surgery for patients with risk factors for failed fusion, e.g. diabetes, renal disease, smoking, alcoholism, etc.
EBGS or UBGS is also used in appendicular skeleton for the treatment of fracture non-unions. A nonunion is considered to be established when after a period of time, since injury at the fracture site shows no visibly progressive signs of healing. Complicated variables are present in fractures, e.g., degree of soft tissue damage, alignment of the bone fragments, vascularity, and quality of the underlying bone stock. Delayed union refers to a decelerating bone healing process, as identified in serial x-rays. (In contrast, nonunion serial x-rays show no evidence of healing.) When lumped together, delayed union and nonunion are sometimes referred to as “un-united fractures.”
In the appendicular skeleton, EBGS or UBGS has been used primarily to treat tibial fractures. According to orthopedic anatomy, the skeleton consists of long bones, short bones, flat bones, and irregular bones. Long bones act as levers to facilitate motion, while short bones function to dissipate concussive forces. Short bones include those composing the carpus and tarsus. Flat bones, such as the scapula or pelvis provide a broad surface area for attachment of muscles. Thus the metatarsal is considered a long bone, while the scaphoid bone of the wrist is considered a short bone. Both the metatarsals and scaphoid bones are at a relatively high risk of nonunion after a fracture.
All bones are composed of a combination of cortical and trabecular (also called cancellous) bone. Cortical bone is always located on the exterior of the bone, while the trabecular bone is found in the interior. Each bone, depending on its physiologic function, has a different proportion of cancellous to trabecular bone. However, at a cellular level, both bone types are composed of lamellar bone and cannot be distinguished microscopically.
Devices to provide EBGS may be noninvasive, with electrodes placed on the skin surface over the area of the bone to be treated. These external EBGS systems are similar to transcutaneous electrical nerve stimulators (TENS). Electrodes on the skin surface are connected to a manually adjusted stimulation controller, typically powered by batteries, which is worn by the patient on a harness or belt. In some cases it is more advantageous to implant all or part of the EBGS device. In implantable systems, the electrodes, constructed on lead wires, are placed directly on the bone, in the area of the bone, or within bone graft material. These leads are then externalized to the skin surface and connected to an external stimulation controller or more typically are arranged in a subcutaneous location where an implantable stimulation controller is subcutaneously implanted and connected to the leads. The invention described in this patent application pertains to EBGS devices in which at least one portion providing direct electrical stimulation to the bone, in the area of the bone, or within bone graft material is either permanently or temporarily implanted. The other portion, the stimulation controller, may or may not be implanted. Devices to provide UBGS are noninvasive systems: the ultrasound transmitter is placed on the skin, coupled to the body using gel, and held over the targeted bone region for the prescribed duration with a prescribed low-intensity ultrasound applied for the treatment duration.
In current practice, implanted electrical energy sources and electrode/lead wire systems are typically used to directly stimulate bone at the site of repair. Such implanted electrode/lead wires exhibit significant problems, such as infection, lead failure, and electrode/lead dislodgement. In certain applications, e.g., EBGS for treatment of bone fusions, leads are implanted at the time of bone repair surgery and left unconnected, awaiting determination of whether the bone will fuse without the aid of electrical stimulation. If the leads were externalized, then the entry/exit site in the skin must be carefully managed to avoid infection. In case of non-fusion, the leads are then connected to a stimulation controller/pulse generator. If the stimulation controller is implanted, this involves yet another procedure.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for EBGS, by achieving a bone stimulation capability without the use of leads connected to a stimulation controller/pulse generator. The invention described in this patent application pertains also to UBGS devices and devices combining both UBGS and EBGS function wherein the ultrasound stimulation generator or the combined ultrasound generator and electrical stimulation controller may or may not be implanted.
Spine Stimulation
Electrical stimulation of spinal nerve roots, the spinal cord, and/or other nerve bundles in the region of the spine, for the purpose of chronic pain management, has been actively practiced since the 1960s. Application of an electrical field to nerve tissue in the spine (i.e., spinal nerve roots and spinal cord bundles) is known to effectively interfere with the transmission of pain signals to the brain. These applications are done today both with externally applied devices and implanted devices. Applying specific electrical pulses to spinal nervous tissue or to peripheral nerve fibers that corresponds to regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, or can in effect block pain transmission to the brain from the pain-afflicted regions. Depending on the individual patient, paresthesia can effectively “mask” certain pain sensations to the brain. Treatment regimens and targeted spinal locations are known in related art through use of current, common stimulation devices and methods. Commonly implanted devices for spinal nerve stimulation are made by such companies as Medtronic, Advanced Neuromodulation Systems, Advanced Bionics, and others.
The spine is an anatomical structure that consists of bones (vertebrae), cartilage (discs), and the spinal cord (a nervous system structure that generally bundles or collects various nerves connecting peripheral areas of the body to the brain). The spine is divided into five regions: (i) cervical (neck), (ii) thoracic (mid-back), (iii) lumbar (lower back), (iv) sacrum, and (v) coccyx (tailbone). The peripheral nervous system refers to the cervical, thoracic, lumbar, and sacral nerve trunks leading away from the spine to all regions of the body. The peripheral nervous system also includes cranial nerves. Pain signals travel between the brain and to other regions of the body using this network of nerves that all travel along the spine as part of the spinal cord.
Transcutaneous electrical nerve stimulation (TENS) is a well known medical treatment used primarily for symptomatic relief and management of chronic intractable pain and as an adjunctive treatment in the management of post surgical and post traumatic acute pain. TENS involves the application of electrical pulses to the skin of a patient, which pulses are generally of a low frequency and are intended to affect the nervous system in such a way as to suppress the sensation of pain, in the area that the electrodes are applied. This typically would be indicated for use in acute or chronic injury or otherwise used as a protective mechanism against pain. Typically, two electrodes are secured to the skin at appropriately selected locations. Mild electrical impulses are then passed into the skin through the electrodes to interact with the nerves lying thereunder. As a symptomatic treatment, TENS has proven to effectively reduce both chronic and acute pain of patients.
Spinal Cord Stimulation (SCS) generally refers to treatments for a variety of medical conditions that apply electrical stimulation directly on nerves, nerve roots, nerve bundles, tissue or regions of the spine. Currently available stimulator systems for SCS are fully implanted electronic devices placed subcutaneously under the skin and connected via insulated metal lead(s) to electrodes which are invasively inserted into or onto the nerves or close to the nerves or spinal cord region. A commonly implanted SCS system contains a battery to power the system. Some implanted SCS systems use an RF wireless connection instead of a battery to power the implanted device. In these RF systems, a receiver device is implanted subcutaneously and a transmitter is worn on the outside of the body. The antenna are tuned to each other and aligned such that control information and power is transmitted to the receiver, which then directs the electrical impulses to the electrodes through the leads. The external transmitter contains batteries to power the transmission. All systems have the capability to externally adjust settings of the implanted system through a programming device.
In SCS and TENS systems, electrical energy is delivered through lead wires to the electrodes. For SCS, implanted electrodes are positioned external to a patient's dura layer (epidural), a structure that surrounds the spinal cord. SCS uses the implanted electrodes to deliver a variety of stimulation modalities with the electric pulse waveform defined by a plurality of variables, including: pulse width, pulse frequency (Hz) or duty cycle, amplitude (V), and sometimes waveform shape (e.g. mono-phasic or bi-phasic).
SCS is used for treatment of headache, migraine headache, or facial pain by stimulating spinal cord including the trigeminal ganglion or ganglia, a trigeminal nerve(s), a branch(es) of a trigeminal nerve(s) (e.g., an ophthalmic nerve(s), a maxillary nerve(s), and/or a mandibular nerve(s)), or a branch(es) of any of these neural structures.
SCS is used for the treatment of chronic pelvic pain due to such conditions as lumbosacral radiculitis, lumbosacral radiculopathy, lumbosacral plexitis, lumbosacral plexopathy, vulvadynia, coccygodynia, peripheral neuritis, and peripheral neuropathy, by applying stimulation to the epidural space of the sacrum on or near selected sacral nerve roots.
SCS is used for chronic pain associated with injury to the spine such as herniated discs or compression fractures. SCS is also used for treating severe chronic pain of a nonspecific origin. Stimulation of nerve tissue in a variety of spinal areas is known to reduce symptoms and enhance the quality of life in patients with chronic pain.
As described above, TENS and SCS devices are battery-powered electronic devices either used transcutaneously (TENS) or implanted (SCS) and connected via insulated metal lead(s) to electrodes which are either placed on the skin (TENS) over the spine or implanted into the dura or epidural layer of the spine (SCS). The implanted electrodes for SCS are positioned on leads that are placed percutaneously, through needle punctures, or through minimally invasive surgical procedures such laminectomy methods, or through direct surgical access to position the electrodes into epidural regions of the spine. Multiple electrodes typically between 4 and 16 are available on the lead and are positioned in the region that is targeted for electrical stimulation. The implanted leads are then subcutaneously tunneled to the pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement.
Many attempts to overcome the complications and limitations imposed by the use of electrical leads have been reported. For example, self-contained implantable microstimulators and remotely powered microstimulators have been described; however each approach suffers from some significant limitation. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three. Due to high use or high energy requirements of the therapeutic stimulation some SCS devices contain rechargeable batteries or are powered remotely with an RF coupling to the controller.
For leadless solutions in other similar stimulation applications, remotely powered devices have previously utilized either radiofrequency (RF) or electromagnetic transformer power transmission. RF energy transmission, unless the transmitting and receiving antennae are placed in close proximity, suffers from inefficiency and limited safe power transfer capabilities, limiting its usefulness in applications where recharging or stimulation must be accomplished at any significant depth (>1-2 cm) within the body, in particular where it is desired to permanently implant both the transmitter and receiver-stimulator. Electromagnetic coupling can more efficiently transfer electrical power, and can safely transfer higher levels of power (devices with capacity in excess of 20 Watts have been produced) but again relies on close proximity between transmitting and receiving coils, or the utilization of relatively large devices for deeper (5-8 cm maximum) implantation.
GI Stimulation
Electrical stimulation of the gastrointestinal system or gastrointestinal tract for the purpose of controlling gastrointestinal activity has been known and actively practiced for several decades. Application of an electrical field between electrodes to gastrointestinal tissue is known to affect the motility and electromotor conduct of the gastric tract; for example, it has been used in the treatment of eating disorders (e.g., obesity, thinness, bulimia, anorexia). For example, applying specific electrical pulses to the selected areas of the stomach can induce a sense of satiety. Disturbances in electromotor activity in diabetic gastroparesis, reflux in the upper digestive tract, and numerous other gastro-enterological functional pathologies can be observed with electrophysiologic sensing and also treated with application of electrical stimulation. Electrical stimulation of other locations in the tract can induce voiding or can be used as a treatment for gastric reflux. These applications are currently practiced using both implanted and externally applied devices.
Depending on the individual patient, gastrointestinal stimulation can effectively modify signal pathways along the tract and thus provide relief of symptoms or control of bodily function. Treatment regimens and targeted gastrointestinal tissue locations are known in related art through use of current, common stimulation devices and methods. Currently, implanted devices for gastrointestinal tissue stimulation are made by companies such as IntraPace and Transneuronix.
The gastrointestinal system is essentially a long tube running from the mouth to the anus consisting of four main sections including the oesophagus, the stomach, the small intestines, and the large intestines. These specialized sections are capable of digesting material place in the mouth and extracting components useful to the body as the material passes through the system. Material that can not be used or that has been processed is expelled from the end of the tube at the anus. The system is under hormonal control, with the presence of food in the mouth triggering off a cascade of hormonal actions; when there is food in the stomach, different hormones activate acid secretion, increased gut motility, enzyme release etc. The stomach is a ‘j’-shaped organ, with two openings—the esophageal and the duodenal, and four regions—the cardia, fundus, body and pylorus. Each region performs different functions; the fundus collects digestive gases, the body secretes pepsinogen and hydrochloric acid, and the pylorus is responsible for mucus, gastrin and pepsinogen secretion. The body uses this arrangement to process food and supply nutrients to the system.
In one early application of electrical gastrointestinal tissue stimulation, an electrode was passed down the esophagus to the stomach and electrical stimulation applied between the electrode and an electrode placed on the patient's abdomen. This induced peristaltic activity within the system. This was an external application of the electrical stimulation system. More recently, the concept has been extended to apply an implantable system into the stomach either as a self-contained stimulator or with electrodes on leads attached to the stomach and then connected to a subcutaneous implanted pulse generator. These systems have been found useful in treatment of obesity both for improving motility in patients and for providing a feeling of satiety to reduce intake.
In the context of this patent application, Gastrointestinal Tissue Stimulation (GTS) refers to treatments for a variety of medical conditions that apply electrical stimulation directly to gastrointestinal tissues. Currently available stimulator systems for GTS are fully implanted electronic devices placed within the stomach or placed subcutaneously under the skin and connected via insulated metal lead(s) to electrodes which are invasively inserted into, around, or onto gastrointestinal tissue. An implanted GTS system contains a battery to power the system. Some implanted GTS systems use an RF wireless connection instead of a battery to power the implanted device. In these RF systems, a receiver device is implanted subcutaneously and a transmitter is worn on the outside of the body. The antenna are tuned to each other and aligned such that control information and power is transmitted to the receiver and then directs the electrical impulses to the electrodes through the leads. The external transmitter contains batteries to power the transmission. All systems have the capability to externally adjust settings of the implanted system through a programming device.
In some GTS systems, electrical energy is delivered through lead wires to the electrodes; in other applications, the self-contained devices incorporate a battery with electrodes disposed on the outer surfaces of the device. For GTS, implanted electrodes are positioned on, around, or in close proximity to the gastrointestinal tissue to be stimulated. GTS uses the implanted electrodes to deliver a variety of stimulation modalities for propagation along the gastrointestinal tissue with the electric pulse waveform defined by a plurality of variables, including: pulse width, pulse frequency (Hz) or duty cycle, amplitude (V), and waveform shape (e.g., mono-phasic or bi-phasic).
GTS is used for treatment of motor disorders of the stomach, such as duodenogastric and gastroesophageal refluxes and relapsing duodenal peptic disorders (ulcer or phlogosis); and for treating obesity and other syndromes related to motor disorders of the stomach.
As described above, GTS devices are battery-powered electronic devices implanted and often connected via insulated metal lead(s) to electrodes which are either placed on the stomach or in the stomach or otherwise within or on the gastrointestinal tissues selected for stimulation. The implanted electrodes for GTS are positioned on leads that may be placed percutaneously, through needle punctures, or through minimally invasive surgical procedures such as laparoscopic methods, or through direct surgical access to position the electrodes on, around, or in proximity to the targeted gastrointestinal tissue. The implanted leads are then subcutaneously tunneled to the pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement. Application of electrodes to the gastrointestinal tissues can be difficult, because the stomach is uniquely designed to pass material through the system; consequently, electrodes are often expelled through the system itself.
Other prior art has attempted to deal with the complications and limitations imposed by the use of electrical leads. For example, self-contained implantable microstimulators and remotely powered microstimulators implanted through the esophagus into gastrointestinal tissue have been described; however, each approach suffers from some significant limitation. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three.
As noted earlier, for leadless solutions in other similar stimulation applications, remotely powered devices have previously utilized either radiofrequency (RF) or electromagnetic transformer power transmission. RF energy transmission, unless the transmitting and receiving antennae are placed in close proximity, suffers from inefficiency and limited safe power transfer capabilities, limiting its usefulness in applications where recharging or stimulation must be accomplished at any significant depth (>1-2 cm) within the body, in particular where it is desired to permanently implant both the transmitter and receiver-stimulator. Electromagnetic coupling can more efficiently transfer electrical power, and can safely transfer higher levels of power (devices with capacity in excess of 20 Watts have been produced), but again relies on close proximity between transmitting and receiving coils, or the utilization of relatively large devices for deeper (5-8 cm maximum) implantation.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for SCS and TENS, by achieving a spinal cord stimulation capability without the use of leads connected to a stimulation controller/pulse generator.
Nerve Stimulation
Electrical stimulation of nerves, nerve roots, and/or other nerve bundles for the purpose of treating patients has been known and actively practiced for several decades. Application of an electrical field between electrodes to stimulate nerve tissues is known to effectively modify signal pathways both with unidirectional and bidirectional stimulation along the nervous system to signal the brain or to signal organs to alleviate symptoms or control function. These applications are currently practiced with, both, externally applied devices and implanted devices. For example, applying specific electrical pulses to nerve tissue or to peripheral nerve fibers that corresponds to regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, or can in effect block pain transmission to the brain from the pain-afflicted regions. Many other examples include electrical stimulation of various branches of the vagus nerve bundle for control of heart rate, mediating hypertension, treating congestive heart failure, controlling movement disorders, treating obesity, treating migraine headache, and effecting the urinary, gastrointestinal, and/or other pelvic structure in order to treat urgency frequency, urinary incontinence, and/or fecal incontinence. Still other branches of the vagus nerve have been used to treat neuropsychiatric disorders. Additionally, applications are also known for electrical stimulation of nerves and nerve bundles in many other specific, selected nerve regions: for example, the pudendal or sacral nerves for controlling the lower urinary tract.
Depending on the individual patient, direct nerve stimulation can effectively modify signal pathways along the nerve, to and from the brain, and to and from organs in the body and thus provide relief of symptoms or control of bodily function. Treatment regimens and targeted nerve locations are known in related art through use of current, common stimulation devices and methods. Commonly implanted devices for nerve stimulation are made by such companies as Cyberonics, Medtronic, Advanced Bionics, and others.
The nervous system is a complex anatomical network that is organized to connect the brain to all areas of the body. The brain uses the nervous system to control bodily processes and adjust the body to its environment. The nervous system is conceptualized by two parts; the central nervous system (CNS), and the peripheral nervous system (PNS). The CNS generally consists of the brain and the spinal cord. The PNS consists of a series of nerves and nerve bundles branching out to all organs and tissue areas of the body. The PNS is connected to the CNS and thus together provides the network of control between the brain and all specific bodily functions. The central nervous system is pervasive throughout the body with individual nerves and nerve bundles reaching to all bodily functions. The PNS consists of the cervical, thoracic, lumbar, and sacral nerve trunks leading away from the spine to all regions of the body. The peripheral nervous system also includes cranial nerves. Sensory and control signals travel between the brain and other regions of the body using this network of nerves that all travel along the spinal cord.
As noted earlier, TENS is a well known medical treatment used primarily for symptomatic relief and management of chronic intractable pain and as an adjunctive treatment in the management of post surgical and post traumatic acute pain. In the context of this application, Specific Nerve Stimulation (SNS) refers to treatments for a variety of medical conditions that apply electrical stimulation directly to nerves, nerve roots, nerve bundles, tissue or regions in proximity to nerves that are in the PNS. Currently available stimulator systems for SNS are fully implanted electronic devices placed subcutaneously under the skin and connected via insulated metal lead(s) to electrodes which are invasively inserted into, around, or onto a nerve or proximate the nerve. A common implanted SNS system contains a battery to power the system. Some implanted SNS systems use an RF wireless connection instead of a battery to power the implanted device. In these RF systems, a receiver device is implanted subcutaneously and a transmitter is worn on the outside of the body. The antenna are tuned to each other and aligned such that control information and power is transmitted to the receiver and then directs the electrical impulses to the electrodes through the leads. The external transmitter contains batteries to power the transmission. All systems have the capability to externally adjust settings of the implanted system through a programming device.
In SNS and TENS systems, electrical energy is delivered through lead wires to the electrodes. For SNS, implanted electrodes are positioned on, around, or in close proximity of the nerve to be stimulated. SNS uses the implanted electrodes to deliver a variety of stimulation modalities including unidirectional and bidirectional propagation along the nerve with the electric pulse waveform defined by a plurality of variables, including, pulse width, pulse frequency (Hz) or duty cycle, amplitude (V), and waveform shape (e.g., mono-phasic or bi-phasic).
SNS is used for treatment of headache, migraine headache, or facial pain by selection of branches in the peripheral nervous system in the cranium or along the vagus nerve bundle. SNS is used for the treatment of chronic pelvic pain due to such conditions as lumbosacral radiculitis, lumbosacral radiculopathy, lumbosacral plexitis, lumbosacral plexopathy, vulvadynia, coccygodynia, peripheral neuritis, and peripheral neuropathy, by applying stimulation to the peripheral nervous system in the sacrum.
SNS is also applied to branches of the vagus nerve in a wide variety of applications, but not limited to the treatment of heart failure; hypertension; obesity; migraine; neuropsychiatric disorders; urinary, gastrointestinal, and/or other pelvic area structures in order to treat urinary urgency, urinary incontinence, and/or fecal incontinence. SNS is also used for severe chronic pain. Stimulation of specific nerves is known to reduce symptoms and enhance the quality of life in patients with chronic pain.
As described above, TENS and SNS devices are battery-powered electronic devices either used transcutaneously (TENS) or implanted (SNS) and connected via insulated metal lead(s) to electrodes which are either placed on the skin (TENS) over the spine or implanted onto, around, or in close proximity to the nerve or nerve bundle selected for stimulation. The implanted electrodes for SNS are positioned on leads that are placed percutaneously, through needle punctures, or through minimally invasive surgical procedures such as laminectomy, or through direct surgical access to position the electrodes on, around, or in proximity to the targeted nerve. On some leads, between 2 and 16 electrodes are available and are positioned in the region that is targeted for electrical stimulation. The implanted leads are then subcutaneously tunneled to the pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement. Application of electrodes to the nerves can be difficult because of the need to precisely locate electrodes for effective therapy.
Other prior art has attempted to deal with the complications and limitations imposed by the use of electrical leads. One such approach is using self-contained microstimulators. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three. Due to high use or high energy requirements of the therapeutic stimulation some SNS devices contain rechargeable batteries or are powered remotely with an RF coupling to the controller.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for selected nerve stimulation, by achieving a nerve stimulation capability without the use of leads connected to a stimulation controller/pulse generator.
Brain Stimulation
Electrical stimulation of brain tissue is a growing treatment for many neurological disorders, including alleviation of Parkinson's and essential tremor diseases, chronic pain, depression, epileptic seizures, motor dysfunction due to stroke, and other emerging applications such as diabetes, obesity, and urinary control. Treatment regimens and targeted brain tissue locations are becoming known in related art through use of current, common stimulation devices and methods. Commonly implanted devices for direct brain stimulation are made by such companies as Medtronic, Cyberonics, and NeuroPace.
Deep Brain Stimulation (DBS) generally refers to treatments for a variety of medical conditions that apply electrical stimulation directly on brain tissue or in regions of the brain. Currently available stimulators for DBS are battery-powered electronic devices implanted under the skin that are connected via insulated metal lead(s) to electrodes that are inserted into or onto the brain. DBS uses the inserted electrodes to deliver a variety of stimulation modalities. For example, continuous high-frequency electrical stimulation is used in areas of the brain including the thalamus, globus pallidus (GPi), or the subthalamic nucleus (STN), or other parts of the brain to control movement disorders. High frequency stimulation of cells in these areas actually shuts them down, helping to rebalance control messages throughout the movement control centers in the brain.
DBS of the thalamus is primarily used to treat disabling tremor, especially tremor that affects one side of the body substantially more than the other. Studies have shown that DBS may significantly reduce tremor in about two thirds of patients with Parkinson's disease (PD). Tremor may not be eliminated, and may continue to cause some impairment. DBS of the globus pallidus is useful in treatment of dyskinesias as well as tremor, and may improve other symptoms, as well. DBS of the subthalamic nucleus may have an effect on most of the main motor features of PD, including bradykinesia, tremor, and rigidity.
Treatment sites for movement disorders may be identified by probing brain tissue and a site predetermined for treatment is selected. As noted for movement disorders, published regions of the brain include, but are not limited to, the ventral intermediate thalamus, subthalamic nucleus, and internal globus pallidus.
Similarly, DBS has been pursued as a treatment for pain for the past 30 years. Peripheral pain signals are transmitted via the spinothalamic tract of the spinal cord and synapse primarily in the thalamus. Thus, the area where they synapse was seen as a prime target for DBS and was the focus of much of the early research. DBS continues to be pursued as a therapy in chronic pain patients. Today, the pain indications that either exist or seem most promising for potential treatment by deep brain stimulation include: neuropathic pain; Complex Regional Pain Syndrome (CRPS), Type II; steady, burning pain; lancinating, shooting pain; tactile hypersensitivity; or partial or complete sensory loss. The targets for DBS for pain typically include the following sites:
Neuropathic Pain                Medial lemniscus        Ventrobasal (VB) area of the thalamus, including the ventral posteromedial (VPM) and the ventral posterolateral (VPL) nuclei        Internal capsule        Motor cortex        Cingulate gyms (also known as cingulate cortex)        Posterior complex of the thalamus (PO)        Ventrolateral nucleus of the thalamus (VL)        
Nociceptive Pain                Periventricular grey (PVG) matter and periaqueductal grey (PAG) matter, which are sometimes simply called periventricular grey and periaqueductal grey        
Similar targets in the brain are emerging for other DBS applications. Published targets for the treatment of depression would include, but are not limited to, one or more of the cerebellar vermis, the anterior cingulate gyms, the dorsal prefrontal cortex, the dorsal raphe nuclei, the median raphe nuclei, and the locus coeruleus. Published targets for the treatment of epilepsy, obesity, and diabetes would include, but are not limited to, the nucleus of tractus solitarius (NTS), the sub thalamic nucleus, the hippocampus, the medial thalamus and the temporal lobe.
Upper regions of the brain, e.g., the cortex, that have been affected by stroke or injury also benefit from stimulation treatments and have been shown to be effective in rehabilitating motor performance of distal extremities. In this stroke rehabilitation treatment the electrode is placed on the dura, the membrane that covers the brain, and used to deliver stimulation to the cortex.
Currently available DBS devices are battery-powered electronic devices implanted under the skin connected via insulated metal lead(s) to electrodes which are inserted into the brain. The brain electrodes are placed into brain tissue via a small cranial hole and then connected to lead extensions which are subcutaneously tunneled between the skull and skin, down the back of the head, and around the neck to the battery-powered pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket in the pectoral region of the chest. Even in cases where the pulse generator may be located under, within, or on the skull the electrodes are still in direct connection to the pulse stimulator using a lead. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, and electrode/lead dislodgement.
Often, DBS devices contain rechargeable batteries due to high use or high energy requirements of the therapeutic stimulation. Implantation of the pulse generator into the skull has been proposed, which addresses the difficult procedural task of tunneling leads and avoids cosmetic appearance issues associated with the subcutaneous leads and pulse generators; however, the lead still must be placed into the brain and connected to the pulse generator.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for DBS, by achieving a brain stimulation capability without the use of leads connected to a stimulation controller/pulse generator.
Cochlear Stimulation
Electrical stimulation in the cochlea of the ear for the purpose of treating patients with hearing loss has been known and actively practiced for several decades. Application of an electrical field between electrodes in the cochlea stimulates cochlear nerve tissues and is known to effectively modify signal pathways to the brain to emulate the sensation of hearing sounds. These applications currently use several components including externally applied parts and implanted parts, collectively referred to as a cochlear implant system (CIS). A cochlear implant system consists of a microphone, which picks up sound from the environment; a sound-speech processor, which selects and arranges sounds picked up by the microphone; a transceiver-stimulator, which receives signals from the sound-speech processor and converts them into electric impulses; and electrodes, which collect the impulses from the transceiver-stimulator and applies them to the cochlea. As the cochlea is stimulated, signals are sent to the brain and interpreted by the brain as sound.
A CIS device does not restore or create normal hearing, nor does it amplify sound like a hearing aid. CIS provides a train of stimulation pulses that are correlated with sound and provides this interpreted pattern of impulses to the brain. The brain is capable of associating these substituted impulses as sound which enables the patient/brain to reform environmental sound recognition and speech recognition. Depending on the individual patient, cochlear stimulation can effectively activate signal pathways along the cochlear nerve, to the brain, and the brain associates these artificially induced impulses with sounds. For example, speech recognition can be accomplished in profoundly deaf patients who learn to associate these stimuli with sound, particularly in combination with reading lips. Treatment regimens and targeted cochlear nerve locations are known in related art through use of current, common stimulation devices and methods. Commonly implanted CIS devices for cochlear nerve stimulation are made by such companies as Med El Medical Electronics, Advanced Bionics, Cochlear Inc. and others.
The hearing system is an anatomical structure that begins at the ear canal. Sound travels through the canal to the ear drum which vibrates and sets in motion bones in the inner ear. This motion causes the fluid in the cochlea to move small hair cells. The hair cells transduce this movement into electrical impulses in the cochlear nerve which sends the impulses to the brain, which then interprets the impulses as sound.
CIS is a well known medical treatment used primarily to restore speech recognition in the patients with conditions that prevent the hair cells in the cochlea from activating, particularly in the profoundly deaf. Microphone, sound-speech processor, transceiver-stimulator, and electrodes are the common components for a conventional CIS device. The Microphone is typically worn behind the ear and configured for wear to hook over the top of the ear or alternatively can be worn on the clothing or placed in a pocket. There is a direct connection from the Microphone, via a wire, to the Sound-speech processor. Alternative embodiments sometimes include the Microphone and the Sound-speech processor in the same device. The Sound-speech processor interprets the sound waves it receives and converts the frequency of the sound waves into trains of pulses with varying pulse durations. The series of pulses is then sent to the Transceiver-stimulator to be converted into electrical signals to be sent between electrodes that are positioned in the cochlea. This series of pulses is communicated from the Sound-speech processor either by direct wired connection to the Transceiver-stimulator or by radiofrequency communication between the two components. The Transceiver-stimulator is implanted subcutaneously between the patient's skin and skull and the Sound-speech processor may be mounted externally on the skull proximate to the Transceiver-stimulator. The Electrodes are connected to the Transceiver-stimulator via a lead that is tunneled from the cochlea to the Transceiver-stimulator. Electrodes are dispersed along the distal end of the lead and positioned throughout the cochlea so that a variety of locations in the cochlea can be stimulated independently. Prior art describes effective processes and algorithms to convert sound into impulse trains and to send those trains to electrodes in selected cochlea regions to stimulate the cochlear nerves.
In CIS systems, electrical energy is delivered through lead wires to the electrodes. CIS implanted electrodes are positioned throughout the spiral structure of the cochlea in order to stimulate different regions in the cochlear nerve. CIS uses the implanted electrodes to deliver a variety of stimulation modalities along the cochlea and thus along the cochlear nerve with the electric pulse waveform defined by a plurality of variables, including but not limited to: pulse width or pulse frequency (Hz).
As described above, CIS devices are battery-powered electronic devices connected via insulated metal lead(s) to electrodes which are placed in the cochlea around or in close proximity to the cochlear nerve or cochlear nerve bundle. The implanted electrodes for CIS are positioned on leads that are placed percutaneously, through needle punctures or through direct surgical access to position the electrodes along the spiral shaped cochlea. A typical application may utilize 16 electrodes (for example, selected and used as 8 pairs of electrodes) positioned in regions that are targeted for electrical stimulation. The implanted leads are then subcutaneously tunneled to the Transceiver-stimulator (also referred to as a controller) that is implanted in a subcutaneous pocket between the skin and the skull. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement. Application of electrodes to the cochlea can be difficult because of the need to locate electrodes for effective therapy. Additionally, the implanted Transceiver-stimulator must be in communication with the external Sound-speech processor. This requires that the implanted Transceiver-stimulator have a percutaneous connection to the Sound-speech processor or that an RF or magnetic coupling be maintained. A percutaneous connection is often a source for infection and wound control.
Other prior art in many stimulation applications has attempted to deal with the complications and limitations imposed by the use of electrical leads. One such attempt is the use of microstimulators. Constant communication from the Speech Processor would be required with the microstimulator imposing further constraints on maintaining a constant communication between the two devices. Due to high use or high energy requirements of the therapeutic stimulation some CIS devices contain rechargeable batteries or are powered remotely with the RF coupling to the controller.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for cochlea stimulation, by achieving a cochlea stimulation capability without direct connection to the Sound-speech processor or without the use of leads connected to a controller.
Hence, it will be beneficial to have a system and method for electrical stimulation of tissue that avoids the problems associated with conventional stimulation systems. Particularly, problems due to leads. Additionally, implantable systems that can remain implanted for longer periods with minimal energy consumption would be particularly desirable.
References
The following patents, all of which are incorporated in this disclosure in their entirety, describe various aspects of using electrical stimulation for achieving various beneficial effects. U.S. Pat. No. 4,026,304 titled “Bone Generating Method and Device” by Levy describes a stimulation protocol that uses a train of pulses rather than constant direct current or voltage, using conventional lead/electrode systems. U.S. Pat. No. 5,441,527 titled “Implantable Bone Growth Stimulator and Method of Operation” by Erickson et al. describes an implantable bone growth stimulation system with electrodes implanted in the region of bone and connected via leads to an implantable stimulator/controller. The following patents describe various methods and systems for the application of ultrasonic energy for achieving beneficial effects related to bone growth or the healing of fractures using ultrasound alone: U.S. Pat. Nos. 6,231,528 and 6,652,473 both titled “Ultrasonic and Growth Factor Bone Therapy: Apparatus and Method” by Kaufman et al., U.S. Pat. Nos. 6,322,527 and 5,556,372 titled “Apparatus for Ultrasonic Bone Treatment” by Talish, U.S. Pat. Nos. 5,752,924 and 5,547,459 titled “Ultrasonic Bone Therapy Apparatus and Method” by Kaufman et al., U.S. Pat. No. 5,496,256 titled “Ultrasonic Bone Healing Device for Dental Application” by Bock et al., U.S. Pat. No. 5,309,898 titled “Ultrasonic Bone Therapy and Assessment Apparatus and Method” by Kaufman et al., and U.S. Pat. No. 4,530,360 titled “Method for Healing Bone Fractures with Ultrasound”. A publication by J D Heckman, J P Ryaby, J McCabe, J J Frey and R F Kilcoyne, “Acceleration of tibial fracture-healing by non-invasive, low-intensity pulsed ultrasound” The Journal of Bone and Joint Surgery, Vol. 76, Issue 1 26-34, 1994, describes the use of a UBGS system.
U.S. Pat. No. 3,835,833 titled “Method for Obtaining Neurophysiological Effects” by Limoge describes delivery and parameters for electrical stimulation in a TENS stimulation system. U.S. Pat. No. 4,690,144 titled “Wireless Transcutaneous Electrical Tissue Stimulator” by Rise et al. also describes delivery, systems, and application parameters for a TENS stimulation system. U.S. Pat. No. 6,735,475 titled “Fully implantable miniature neurostimulator for stimulation as a therapy for headache and/or facial pain” by Whitehurst et al. describes an implantable microstimulator used for treatment of pain in peripheral nerves generally in the skull or the cervical regions of the spine. U.S. Pat. No. 6,748,276 titled “Neuromodulation therapy system” by Daignault et al. describes an implantable SCS system that uses an external RF communication to adjust delivery of therapy. U.S. Pat. No. 6,027,456 titled “Apparatus and method for positioning spinal cord stimulation leads” by Feler et al. describes approaches to the implantation of leads into the dorsal column of a patient. U.S. Pat. No. 5,938,690 titled “Pain management system and method” by Law et al. describes methods for determining and optimizing treatment parameters and regimens for by mapping patient responses to test stimulation patterns. U.S. Pat. No. 6,002,965 titled “Epidural nerve root stimulation” by Feler et al. describes treating pelvic pain by application of stimulation in the sacral and lumbar regions of the spine.
U.S. Pat. No. 3,522,811 titled “Implantable Nerve Stimulator and Method of Use” by Schwartz et al. describes an implantable application for stimulation of the carotid sinus nerve as a treatment for hypertension. U.S. Pat. No. 6,615,081 titled “Apparatus and method for adjunct (add-on) treatment of diabetes by neuromodulation with an external stimulator” by Boveja describes an implantable application for stimulation of the vagus nerve as a treatment for diabetes. U.S. Pat. No. 6,684,105 titled “Treatment of disorders by unidirectional nerve stimulation” by Cohen et al. describes an application of electrical stimulation of nerves in unidirectional and bidirectional propagation of the electrical treatment along the nerve. U.S. Pat. No. 5,282,468 titled “Implantable neural electrode” by Klepinski describes an implantable neural electrode for stimulation in contact with nerve tissue. U.S. Pat. No. 5,330,515 titled “Treatment of pain by vagal afferent stimulation” by Rutecki et al. describes an implantable application for stimulation of the vagus nerve as a treatment for pain. U.S. Pat. No. 6,622,038 titled “Treatment of movement disorders by near-diaphragmatic nerve stimulation” by Barrett et al. describes an implantable application for stimulation of branches of the vagus nerve near the diaphragm as a treatment for movement disorders such as epileptic seizure, essential tremor, etc. U.S. Pat. No. 6,622,041 titled “Treatment of congestive heart failure and autonomic cardiovascular drive disorders” by Terry et al. describes an implantable application for stimulation of the cardiac branch of the vagus nerve as a treatment for congestive heart failure. U.S. Pat. No. 5,188,104 titled “Treatment of eating disorders by nerve stimulation” by Wernicke et al. describes an implantable application for stimulation of the vagus nerve as a treatment for eating disorders. U.S. Pat. No. 6,879,859 titled “External pulse generator for adjunct (add-on) treatment of obesity, eating disorders, neurological, neuropsychiatric, and urological disorders” by Bovej a describes an external application for stimulation of the vagus nerve as a treatment for a variety of conditions for example, obesity, urological disorders, etc. where the application of the stimulation can be turned off and on by the patient or caregiver. U.S. Pat. No. 6,505,074 titled “Method and apparatus for electrical stimulation adjunct (add-on) treatment of urinary incontinence and urological disorders using an external stimulator” by Boveja describes an external application for stimulation of the sacral nerves and its branches as a treatment for a variety of urological conditions. U.S. Pat. No. 5,215,086 titled “Therapeutic treatment of migraine symptoms by stimulation” by Terry et al. describes an implantable application for stimulation of the vagus nerve as a treatment for migraine headache. U.S. Pat. No. 5,531,778 titled “Circumneural electrode assembly” by Maschino et al. describes an electrode design for attachment to a nerve. U.S. Pat. No. 5,251,634 titled “Helical nerve electrode” by Weinberg describes an electrode design for attachment to a nerve. U.S. Pat. No. 6,622,047 titled “Treatment of neuropsychiatric disorders by near-diaphragmatic nerve stimulation” by Barrett et al. describes an implantable application for stimulation of the vagus nerve as a treatment for neuropsychiatric disorders. U.S. Pat. No. 7,047,078 titled “Methods for stimulating components in, on, or near the pudendal nerve or its branches to achieve selective physiologic responses” by Boggs et al. describes an implantable application for stimulation of the pudenal nerve to control physiologic responses, for example for control of the urinary tract. U.S. Pat. No. 6,002,965 titled “Epidural nerve root stimulation” by Feler et al. describes treating pelvic pain by application of stimulation of nerves in the sacral and lumbar regions of the spine.
U.S. Pat. No. 5,716,377 titled “Method of Treating Movement Disorders by Brain Stimulation” by Rise et al. describes a typical implantable DBS system for treating movement disorders such as Parkinson's. U.S. Pat. No. 7,013,177 titled “Treatment of Pain by Brain Stimulation” by Whitehurst et al. describes an implantable DBS system that uses electrical stimulation in the form of a microstimulator in combination with drug delivery for the treatment of pain. U.S. Pat. No. 7,010,351 titled “Methods and apparatus for effectuating a lasting change in a neural-function of a patient” by Firlik et al. describes a DBS system used to treat or effectuate changes to neural function particularly by stimulation in the region of the cortex. U.S. Pat. No. 6,427,086 titled “Means and method for the intracranial placement of a neurostimulator” by Fischell et al. describes a DBS device implanted in the skull. U.S. Pat. No. 6,016,449 titled “System for treatment of neurological disorders” by Fischell et al. describes the use of a DBS device for the treatment of epilepsy. U.S. Pat. No. 5,782,798 titled “Techniques for treating eating disorders by brain stimulation and drug infusion” by Rise describes a DBS system for treating eating disorders with electrical stimulation in regions of the brain.
U.S. Pat. No. 3,751,605 titled “Method for Inducing Hearing” by Michelson describes methods for inducing the sensation of intelligible hearing by direct electrical excitation of the auditory nerve endings distributed along the basilar membrane within the cochlea. U.S. Pat. No. 4,400,590 titled “Apparatus for multichannel cochlear implant hearing aid system” by Michelson describes an intra-cochlear electrode array for electrically stimulating predetermined locations of the auditory nerve within the cochlea of the ear. U.S. Pat. No. 4,819,647 titled “Intracochlear electrode array” by Byers et al. also describes an intra-cochlear electrode array for electrically stimulating the cochlea of the ear. U.S. Pat. No. 6,671,559 titled “Transcanal, transtympanic cochlear implant system for the rehabilitation of deafness and tinnitus” by Goldsmith et al. describes an implantable application for cochlea stimulation using a system that couples communication and energy via RF or inductive coupling. U.S. Pat. No. 6,889,094 titled “Electrode array for hybrid cochlear stimulator” by Kuzma describes an implantable cochlear electrode array.
U.S. Pat. No. 4,690,144 titled “Wireless Transcutaneous Electrical Tissue Stimulator” by Rise et al. describes a transcutaneous system with electrodes attached to the skin and an external controller providing for electrical field stimulation to body tissue. U.S. Pat. No. 5,405,367 titled “Structure and Method of Manufacture of an Implantable Microstimulator” by Schulman et al. describes an implantable microstimulator used generally for stimulation of tissue. U.S. Pat. No. 6,037,704 titled “Ultrasonic Power Communication System” by Welle describes the use of ultrasound energy transfer from a transmitter to a receiver for purposes of powering a sensor or actuator without being connected by a lead/wire. U.S. Pat. No. 6,366,816 titled “Electronic Stimulation Equipment with Wireless Satellite Units” by Marchesi describes a tissue stimulation system based on a wireless radio transmission requiring the charging of a battery at the receiver and separate command signals used to control the delivery of stimulation. German patent application DE4330680A1 titled “Device for Electrical Stimulation of Cells within a Living Human or Animal” by Zwicker describes a general approach to power transfer using acoustic energy for tissue stimulation.
Many designs have been disclosed to eliminate leads in stimulation systems or to develop systems that are locally implanted with integrated electrodes. For example, the following patents describe various stimulator designs: U.S. Pat. No. 3,943,936 to Rasor describes a stimulator where a self-powered, self-contained pacer and stimulator implanted in the body and the system takes advantage of the body's movement to derive the energy needed for stimulation; U.S. Pat. No. 3,486,506 to Auphan describes a spring driven cardiac stimulator where the motion of the heart is captured in a balance wheel, which in turns oscillates a permanent magnet motor that induces electric pulses that could be applied to stimulate the heart; U.S. Pat. No. 5,193,540 to Schulman discloses an implantable microstimulator that could be expelled from a hypodermic needle and derives energy by RF induction; U.S. Pat. No. 5,358,514 to Schulman describes an implantable micro-miniature stimulator and/or sensor with self-attaching electrodes; U.S. Pat. No. 5,405,367 to Schulman describes a structure and method of manufacture of an implantable microstimulator that is described in U.S. Pat. No. 5,358,514; U.S. Pat. No. 5,411,535 to Fujii describes a cardiac pacemaker using wireless transmission; U.S. Pat. No. 5,814,089 to Stokes discloses a leadless multisite implantable stimulus and diagnostic system that uses high frequency signals comprising a power component derived from a power source and using this power to stimulate tissue; U.S. Pat. No. 6,141,588 to Cox describes an implantable stimulation system with multiple stimulators where the stimulators are described as satellites in wireless communication with a “planet” control unit and receive instructions and electric power wirelessly; U.S. Pat. No. 6,654,638 to Sweeney discloses an implantable electrode that can be activated by ultrasound; U.S. Pat. No. 7,003,350 to Denker describes intravenous cardiac pacing system with wireless power supply based on RF signals; and U.S. patent application Ser. No. 10/632,265 to Penner discloses an implantable electrode that can be activated by ultrasound.